diff --git a/java/bootclasspath_fragment.go b/java/bootclasspath_fragment.go
index ced0048..8f18790 100644
--- a/java/bootclasspath_fragment.go
+++ b/java/bootclasspath_fragment.go
@@ -139,6 +139,74 @@
 	BootclasspathFragmentsDepsProperties
 }
 
+type SourceOnlyBootclasspathProperties struct {
+	Hidden_api struct {
+		// Contains prefixes of a package hierarchy that is provided solely by this
+		// bootclasspath_fragment.
+		//
+		// This affects the signature patterns file that is used to select the subset of monolithic
+		// hidden API flags. See split_packages property for more details.
+		Package_prefixes []string
+
+		// The list of split packages provided by this bootclasspath_fragment.
+		//
+		// A split package is one that contains classes which are provided by multiple
+		// bootclasspath_fragment modules.
+		//
+		// This defaults to "*" - which treats all packages as being split. A module that has no split
+		// packages must specify an empty list.
+		//
+		// This affects the signature patterns file that is generated by a bootclasspath_fragment and
+		// used to select the subset of monolithic hidden API flags against which the flags generated
+		// by the bootclasspath_fragment are compared.
+		//
+		// The signature patterns file selects the subset of monolithic hidden API flags using a number
+		// of patterns, i.e.:
+		// * The qualified name (including package) of an outermost class, e.g. java/lang/Character.
+		//   This selects all the flags for all the members of this class and any nested classes.
+		// * A package wildcard, e.g. java/lang/*. This selects all the flags for all the members of all
+		//   the classes in this package (but not in sub-packages).
+		// * A recursive package wildcard, e.g. java/**. This selects all the flags for all the members
+		//   of all the classes in this package and sub-packages.
+		//
+		// The signature patterns file is constructed as follows:
+		// * All the signatures are retrieved from the all-flags.csv file.
+		// * The member and inner class names are removed.
+		// * If a class is in a split package then that is kept, otherwise the class part is removed
+		//   and replaced with a wildcard, i.e. *.
+		// * If a package matches a package prefix then the package is removed.
+		// * All the package prefixes are added with a recursive wildcard appended to each, i.e. **.
+		// * The resulting patterns are sorted.
+		//
+		// So, by default (i.e. without specifying any package_prefixes or split_packages) the signature
+		// patterns is a list of class names, because there are no package packages and all packages are
+		// assumed to be split.
+		//
+		// If any split packages are specified then only those packages are treated as split and all
+		// other packages are treated as belonging solely to the bootclasspath_fragment and so they use
+		// wildcard package patterns.
+		//
+		// So, if an empty list of split packages is specified then the signature patterns file just
+		// includes a wildcard package pattern for every package provided by the bootclasspath_fragment.
+		//
+		// If split_packages are specified and a package that is split is not listed then it could lead
+		// to build failures as it will select monolithic flags that are generated by another
+		// bootclasspath_fragment to compare against the flags provided by this fragment. The latter
+		// will obviously not contain those flags and that can cause the comparison and build to fail.
+		//
+		// If any package prefixes are specified then any matching packages are removed from the
+		// signature patterns and replaced with a single recursive package pattern.
+		//
+		// It is not strictly necessary to specify either package_prefixes or split_packages as the
+		// defaults will produce a valid set of signature patterns. However, those patterns may include
+		// implementation details, e.g. names of implementation classes or packages, which will be
+		// exported to the sdk snapshot in the signature patterns file. That is something that should be
+		// avoided where possible. Specifying package_prefixes and split_packages allows those
+		// implementation details to be excluded from the snapshot.
+		Split_packages []string
+	}
+}
+
 type BootclasspathFragmentModule struct {
 	android.ModuleBase
 	android.ApexModuleBase
@@ -147,6 +215,8 @@
 
 	properties bootclasspathFragmentProperties
 
+	sourceOnlyProperties SourceOnlyBootclasspathProperties
+
 	// Collect the module directory for IDE info in java/jdeps.go.
 	modulePaths []string
 }
@@ -180,7 +250,7 @@
 
 func bootclasspathFragmentFactory() android.Module {
 	m := &BootclasspathFragmentModule{}
-	m.AddProperties(&m.properties)
+	m.AddProperties(&m.properties, &m.sourceOnlyProperties)
 	android.InitApexModule(m)
 	android.InitSdkAwareModule(m)
 	initClasspathFragment(m, BOOTCLASSPATH)
@@ -590,7 +660,7 @@
 	// TODO(b/192868581): Remove once the source and prebuilts provide a signature patterns file of
 	//  their own.
 	if output.SignaturePatternsPath == nil {
-		output.SignaturePatternsPath = buildRuleSignaturePatternsFile(ctx, output.AllFlagsPath)
+		output.SignaturePatternsPath = buildRuleSignaturePatternsFile(ctx, output.AllFlagsPath, []string{"*"}, nil)
 	}
 
 	// Initialize a HiddenAPIInfo structure.
@@ -659,7 +729,20 @@
 func (b *BootclasspathFragmentModule) produceHiddenAPIOutput(ctx android.ModuleContext, contents []android.Module, input HiddenAPIFlagInput) *HiddenAPIOutput {
 	// Generate the rules to create the hidden API flags and update the supplied hiddenAPIInfo with the
 	// paths to the created files.
-	return hiddenAPIRulesForBootclasspathFragment(ctx, contents, input)
+	output := hiddenAPIRulesForBootclasspathFragment(ctx, contents, input)
+
+	// If the module specifies split_packages or package_prefixes then use those to generate the
+	// signature patterns.
+	splitPackages := b.sourceOnlyProperties.Hidden_api.Split_packages
+	packagePrefixes := b.sourceOnlyProperties.Hidden_api.Package_prefixes
+	if splitPackages != nil || packagePrefixes != nil {
+		if splitPackages == nil {
+			splitPackages = []string{"*"}
+		}
+		output.SignaturePatternsPath = buildRuleSignaturePatternsFile(ctx, output.AllFlagsPath, splitPackages, packagePrefixes)
+	}
+
+	return output
 }
 
 // produceBootImageFiles builds the boot image files from the source if it is required.
diff --git a/java/hiddenapi_modular.go b/java/hiddenapi_modular.go
index f1e30f3..0cc960d 100644
--- a/java/hiddenapi_modular.go
+++ b/java/hiddenapi_modular.go
@@ -943,13 +943,22 @@
 
 // buildRuleSignaturePatternsFile creates a rule to generate a file containing the set of signature
 // patterns that will select a subset of the monolithic flags.
-func buildRuleSignaturePatternsFile(ctx android.ModuleContext, flagsPath android.Path) android.Path {
+func buildRuleSignaturePatternsFile(ctx android.ModuleContext, flagsPath android.Path, splitPackages []string, packagePrefixes []string) android.Path {
 	patternsFile := android.PathForModuleOut(ctx, "modular-hiddenapi", "signature-patterns.csv")
 	// Create a rule to validate the output from the following rule.
 	rule := android.NewRuleBuilder(pctx, ctx)
+
+	// Quote any * in the packages to avoid them being expanded by the shell.
+	quotedSplitPackages := []string{}
+	for _, pkg := range splitPackages {
+		quotedSplitPackages = append(quotedSplitPackages, strings.ReplaceAll(pkg, "*", "\\*"))
+	}
+
 	rule.Command().
 		BuiltTool("signature_patterns").
 		FlagWithInput("--flags ", flagsPath).
+		FlagForEachArg("--split-package ", quotedSplitPackages).
+		FlagForEachArg("--package-prefix ", packagePrefixes).
 		FlagWithOutput("--output ", patternsFile)
 	rule.Build("hiddenAPISignaturePatterns", "hidden API signature patterns")